Certain automotive engines are equipped with a low pressure fuel injection system having a fuel injector which delivers fuel in timed pulses into the engine air induction passage above the throttle. Such a fuel injection system, known as a throttle body injection system or a TBI system, has been provided both in a one barrel assembly in which all of the air flow to the engine is controlled by a single throttle and a single injector delivers fuel above the throttle, and in a side-by-side two barrel assembly in which each of the parallel air induction passages is controlled by a throttle and has an injector delivering fuel above the throttle.
In a system of this nature, fuel flow is conventionally controlled by varying the duration of the timed fuel delivery pulses: when increased fuel delivery is desired, the injector is energized for a longer period of time to increase the duration of the fuel delivery pulse; when decreased fuel delivery is desired, the injector is energized for a shorter period of time to decrease the duration of the fuel delivery pulse. It will be appreciated, of course, that variations in the pressure of the fuel supplied to the injector also will affect fuel delivery by the injector. Accordingly, in order to provide predictable and repeatable fuel delivery by the injector in response to the duration of the fuel delivery pulses, the fuel supply pressure is controlled in a selected manner, generally by maintaining a constant supply pressure.
Thus for example, in the one barrel TBI assembly, the injector is mounted in an injector chamber, and fuel flows through the injector chamber to a nearby pressure regulator which maintains a substantially constant supply pressure in the injector chamber. Similarly, in the two barrel TBI assembly, the injectors are mounted in separate injector chambers, and fuel flows in parallel through the injector chambers to a nearby pressure regulator which maintains the same substantially constant supply pressure in the two injector chambers.
It should be noted that in addition to controlling the supply pressure to the injectors, the TBI pressure regulator also allows a continuous circulation of fuel through the TBI assembly. The circulating fuel cools the injectors and other portions of the assembly to prevent formation of fuel vapor which might otherwise affect fuel delivery by the injectors.
In another embodiment of the TBI system, it is desired to mount two single barrel TBI assemblies at remotely spaced locations on an engine intake manifold. In a system of this nature, a single pressure regulator necessarily would be located remotely from at least one of the injector chambers and therefore could not prevent fluctuations in the supply pressure for that injector. On the other hand, a pair of pressure regulators each located closely adjacent an associated injector chamber could prevent fluctuations in the supply pressure for the injectors, but the supply pressure for the two injectors would not necessarily be the same and most of the fuel would circulate through and cool only the assembly with the lower supply pressure.